Method of metathesis of alkanes and catalyst

ABSTRACT

A process for the metathesis of linear or branched starting alkanes involves, first, grafting metal atoms in the form of hydrides to a solid oxide, such that the grafted metal atoms are dispersed over the solid oxide, which effects a solid catalyst, and second, reacting the starting alkanes over the solid catalyst.

The present invention relates to a process for the metathesis ofalkanes.

It is well known that alkanes commonly known as paraffins are moleculeswhich are difficult to convert because of their chemical inertia.

It is known to convert alkanes by hydrogenolysis reactions ofcarbon—carbon bonds. It has been possible, over certain metal catalysts,simultaneously to observe homologation reactions of alkanes but thelatter always remain very minor reactions with respect to thehydrogenolysis reactions. This is because these reactions are alwayscarried out in the presence of hydrogen, at temperatures varying from250 to 350° C., in contact with catalysts based on transition metals inmassive form or in the form of films or else in the form of metalparticles supported on oxides. The best results seem to have beenobtained by Donohoe, Clarke and Rooney with linear C₅ to C₇ alkanes overtungsten film (J. Chem. Soc. Farad. Trans. I, 1980, 76, 345; J. Chem.Soc. Chem. Commun., 1979, 648); the reaction proves to be slower by anorder of magnitude with branched alkanes and does not take place withcyclic alkanes. Sarkany has also studied the homologation of butane andvarious C₄ or C₅ alkanes over catalysts of nickel black, Ni/SiO₂,platinum black, Pt/SiO₂ or Pd/Al₂O₃ type (J. Chem. Soc. Farad. Trans. I,1986, 82, 103; J. Catal., 1984, 89, 14); this reaction is also favouredin the case of linear alkanes with respect to branched alkanes butalways remains a minor process beside isomerization reactions (forexample of butane to isobutane over Pt/SiO₂) or hydrogenolysis reactions(over Ni/SiO₂). The homologation-aromatization of pentane orcyclopentane to benzene has been reported by Peter and Clarke overrhodium film alloyed with copper, tin, gold or silver (J. Chem. Soc.Farad. Trans. I, 1976, 72, 1201) and by Sarkany over Ni/SiO₂ (J. Chem.Soc. Chem. Commun., 1980, 525); only alloyed rhodium films give asuitable selectivity for benzene while hydrogenolysis remainspredominant with nickel catalysts, even for reduced conversions. Thus,the performances of these known homologation reactions of alkanes remainvery modest or linked to an aromatization process.

Nevertheless, if it were known how to convert alkanes into their higherhomologues, this would constitute a means for enhancing the value ofcertain petroleum fractions, such as in particular the C₄ or C₅fractions. It would be possible to envisage numerous applications in thefield of oils, fuels, polymers or organic chemical synthesis, making itpossible to lengthen side chains or to obtain higher branchedhydrocarbons by other routes than acidic or superacidic catalysis. Thisis because it is known that high octane numbers are particularly desiredin the field of fuels. It is also well known that low molecular weightalkanes cannot be enhanced in value to any significant extent, whereasheavier alkanes are of greater commercial interest.

The object of the present invention is thus to provide a process whichmakes it possible to convert alkanes into their higher and lowerhomologues with high selectivity.

Another object of the invention is to provide such a process which has awide field of application which can cover, simultaneously, the fields ofoils, fuels, polymers or organic chemical synthesis, the elongation ofthe side chains of compounds comprising them or the production of higherbranched hydrocarbons. Such an object is thus in particular theenhancement in value of light alkanes to heavier alkanes of greateradvantage industrially.

Another object of the invention is to provide such a process which canbe employed under moderate operating conditions, namely in particular atrelatively low temperature and relatively low pressure.

Yet another object of the invention is to provide novel catalysts of usein the context of the process for the metathesis of alkanes.

It has been discovered, which is the subject-matter of the presentinvention, that it is possible, by using the catalysts of the invention,to carry out the metathesis of alkanes to higher and lower homologueswith high selectivity and even at low temperature, in particular attemperatures of less than 200° C.

A subject-matter of the invention is therefore a process for themetathesis of linear or branched starting alkanes, in which process thestarting alkane or alkanes is/are reacted over a solid catalystcomprising a metal hydride grafted to and dispersed over a solid oxide.It seems probable that this catalyst acts as catalytic precursor. Whenit is brought into the presence of alkanes, this catalyst has a tendencyto form an alkylmetal complex which would be the catalytically activespecies.

The reaction according to the invention provides for the metathesis ofsigma C—C bonds and the conversion of an alkane into its higher andlower homologues. Thus, starting with an alkane, for example ethane, itis possible to obtain, directly and successively, all the higher alkanesand in particular branched alkanes.

The reaction can be written according to the equation:

C_(n)H_(2n+2)→C_(n−i)H_(2(n−i)+2)+C_(n+i)H_(2(n+i)+2)  (I)

i=1, 2, 3 . . . n−1

The invention thus makes possible the direct conversion of light alkanesinto heavier alkanes and thus an enhancement in value of these lightalkanes, in particular C₄-C₅ petroleum fractions. It also makes possiblethe elongation of side hydrocarbon-comprising chains on certain cycliccompounds.

In an entirely preferred way, the catalysts according to the inventionare obtained from an organometallic complex of following formula (II):

MR_(a)  (II)

where

M is a transition metal selected from those of groups 5 and 6 of thePeriodic Classification of the Elements, preferably from tantalum,tungsten and chromium;

the R groups are identical or different, saturated or unsaturated,preferably C₁, to C₁₀, hydrocarbon-comprising ligands bonded to the M byone or more carbons (it being possible for the metal-carbon bonds to besimple, double or triple bonds);

a is less than or equal to the valency of M, which is 5 or 6.

Mention may in particular be made, among the appropriate ligands, ofmethyl, neopentyl, neopentylidene, neopentylidyne, benzyl or theirmixtures, for example neopentyl-neopentylidene orneopentyl-neopentylidine.

The neopentyl-neopentylidene and neopentyl-neopentylidine mixtures areparticularly advantageous when complexed with tantalum, respectivelytungsten.

According to an embodiment which is particularly appropriate to the useof the solid catalyst, the dispersing and the grafting of theorganometallic compound are carried out over and to a very anhydroussolid oxide. The solid oxide, for example silica, is subjected to anexhaustive heat treatment (with the intention of providing fordehydration and dehydroxylation), in particular between 200 and 1100° C.for several hours (for example, from 10 to 20 hours). Of course, aperson skilled in the art will take care not to exceed the degradationtemperature or stability limit temperature of the solid oxide which hehas chosen to use. For silica, the dehydration is carried out between200 and 500° C., preferably in the vicinity of 500° C., for a simpledehydration reaction or at a temperature greater than 500° C., if it isdesired additionally to obtain the formation of surface siloxanebridges.

The transfer of the complex onto the solid oxide can be carried out inparticular by sublimation or in solution.

In the case of sublimation, the organometallic complex in the solidstate is heated under vacuum and under temperature conditions whichprovide for its sublimation and its migration in the vapour state ontothe solid oxide, which itself is preferably in the pulverulent state orin the form of pellets or the like. The sublimation is carried out inparticular between 50 and 150° C., preferably in the vicinity of 80° C.The deposition can be monitored, for example by infrared spectroscopy.

The grafting takes place by reaction of the complex with the functionalgroups of the support (OH, Si—O—Si, and the like). The grafting willpreferably be carried out at a temperature greater than or equal toambient temperature.

It may be desirable to remove the excess complex which has not reactedand which has been simply adsorbed at the surface of the oxide by areverse sublimation.

A treatment under hydrogen or in the presence of another appropriatereducing agent is subsequently carried out under conditions resulting inthe conversion of the metal atoms to hydrides by hydrogenolysis of thehydrocarbon-comprising ligands. It is possible in particular to operateunder a pressure of between 10⁻² and 100 bar but preferably atatmospheric pressure. As regards the temperature, it is possible tooperate between 25 and 400°C., more generally in the vicinity of 150° C.The reaction is carried out for a sufficient period of time which canrange, for example, from 1 h to 24 h, in particular from 10 to 20 h, inparticular approximately 15 h.

In the general method which has just been described, it is possible toreplace the sublimation by a reaction in solution. In this case, theorganometallic complex is in solution in a conventional organic solvent,such as benzene, toluene, pentane or ether, the condition being to be ina very anhydrous medium. The reaction is carried out by suspending solidoxide, preferably pulverulent oxide, in this metal complex solution oralternatively by any other method which provides for appropriate contactbetween the two media. The reaction can be carried out at ambienttemperature and more generally between 25 and 150° C.

The catalysts according to the invention exhibit the following notablecharacteristics:

very good dispersion of the metal over the solid oxide, this dispersionbeing largely, predominantly or completely monoatomic as regards themetal;

the bonding between the metal atom and the, oxygen of the solid oxide isvery strong and makes it possible to maintain the state of dispersionachieved;

the metal attached to the support is in an advanced state ofunsaturation; its d electron shell is highly deficient in electrons(less than 16 electrons); in the cases observed, approximately 10electrons are present.

Other precursor complexes can be used insofar as they result in a truehydride by the method described or by any other synthetic route.

The metal complexes according to the invention are supported on orgrafted to and dispersed over a solid oxide; mention may preferably bemade, among the supports of oxide type, of silica, alumina,silicas-aluminas or niobium oxide, zeolites, without the list beinglimiting.

Among these catalysts, tantalum, tungsten or chromium hydrides graftedto silica or silica-alumina are more particularly recommended.

A subject-matter of the invention is therefore the use of these metalcomplexes, dispersed over and grafted to solid oxide, in the manufactureof a catalyst for the metathesis of alkanes.

Linear alkanes suitable for the implementation of the process accordingto the invention can be selected from alkanes comprising at least twocarbon atoms; it being possible for the process to be applied to alkanesup to C₃₀ and beyond; preferred examples of alkanes are ethane, propane,butane, pentane, and the like.

The process can also be applied to branched alkanes comprising fourcarbon atoms or more, in particular up to C₃₀; preferred examples are:isobutane, isopentane, 2-methylpentane, 3-methylpentane,2,3-dimethylbutane, and the like.

The process can also be applied to cyclic hydrocarbons (compounds withone or more rings), for example aromatic rings or saturated rings,substituted by at least one linear or branched alkane chain. Mention maybe made, by way of example, of cyclic hydrocarbons substituted with atleast one linear or branched alkane chain according to the generalformula (III):

where:

x is greater than or equal to 2, preferably between 2 and 20;

y is greater than or equal to 0, preferably between 0 and 29.

In these cases, the reaction affects the alkane chains.

The hydrocarbons according to the invention, that is to say saturatedlinear, branched and/or substituted cyclic (in this case, the reactiontaking place on the substitution alkanes) hydrocarbons, can be subjectedto the reaction for the metathesis of sigma carbon—carbon bonds withthemselves or in the presence of another hydrocarbon.

The process can also be applied to similar compounds comprising one ormore heteroatoms, such as O, S or N.

A first method for the application of the process according to theinvention consists in reacting the linear, branched or substitutedcyclic hydrocarbon by a metathesis reaction with itself, in order toobtain higher and lower homologous alkanes.

A second method consists in reacting with each other at least twohydrocarbons selected from linear, branched and substituted cyclic, soas to obtain branched or substituted cyclic hydrocarbons resulting fromreactions for the metathesis of sigma carbon—carbon bonds. More simply,the metathesis reaction is carried out on a mixture of at least twodifferent hydrocarbons.

The reaction for the metathesis of linear, branched or substitutedcyclic alkanes is preferably carried out by passing the alkane in thegas phase over the solid catalyst; the gas-phase reaction can be carriedout at atmospheric pressure or above, but at a pressure less than orequal to the condensation pressure of the isolated alkane or of theheaviest alkane when there are several starting alkanes. The reactioncan also be carried out in the liquid phase in the alkane or in amixture of alkanes with the catalyst in suspension. The reaction canalso be carried out in the presence of an inert gas, such as,preferably, nitrogen, helium or argon.

The metathesis reaction according to the invention can be carried out ina batch reactor, that is to say with a fixed amount of reactantsintroduced for a complete reaction cycle, in a recycling reactor, inwhich the alkanes obtained can in particular be recycled, or in acontinuous reactor, that is to say with passage of the liquid or gaseousreactant flows over a catalyst bed.

The metathesis reaction can be carried out at temperatures varying from25 to 300° C. but preferably between 100 and 200° C. The pressure can bebetween 10⁻² and 100 bar. It is preferable to operate starting fromatmospheric pressure.

The reaction for the metathesis of a given alkane results in theformation of its higher and lower alkanes, as shown in the equation (I),with a high selectivity for higher alkane, the attractive compound.

The advantage being in particular in forming higher alkanes, it ispossible to provide for recycling the alkanes obtained during thereaction. It can relate both to the recycling of the lower alkane and tothe recycling of the higher alkane obtained, in order to continue thereaction towards the production of ever higher alkanes.

It is optionally possible to provide for the separation between higheralkanes and lower alkanes, for example with the intention of recyclingthe lower alkane or the higher alkane. It is, of course, also possibleto recycle the combination, the reaction according to the inventionadvantageously taking place preferentially on the lower alkanes.

The metathesis reaction according to the invention finds numerousapplications in the fields defined above. One of the main applicationsrelates to the production of a high octane number for fuels, in order toimprove the stability towards compression. The process according to theinvention makes it possible to enrich fuels with heavy and/or branchedalkanes, which helps to increase the stability towards compression.

The invention will now be described in more detail using non-limitingembodiments.

EXAMPLE 1

Preparation of the Tantalum Hydride Catalyst:

The [Ta]_(s)—H surface tantalum hydride catalyst can be prepared in thefollowing way: tris(neopentyl)neopentylidenetantalumTa[—CH₂—CMe₃]₃—[═CH—CMe₃] is sublimed at 80° C. in a glass reactor oversilica dehydroxylated beforehand at 500° C., so as to graft the tantalumcomplex by a reaction at 25° C. with one or more hydroxyl groups of thesilica surface, which reaction also produces neopentane:

≡SiOH+Ta[—CH₂—CMe₃]₃[═CH—CMe₃]→≡SiO—Ta[—CH₂—CMe₃]₂[═CH—CMe₃]+(≡SiO)₂—Ta[—CH₂—CMe₃][═CH—CMe₃]+CMe4

The mixture of neopentyl-neopentylidene complexes obtained:

≡SiO—Ta[—CH₂—CMe₃]₂[═CH—CMe₃] and (≡SiO)₂—Ta[—CH₂—CMe₃][═CH—CMe₃]

is subsequently treated under hydrogen at atmospheric pressure at 150°C. for 15 h, so as to form the supported tantalum hydride species; thisreaction is accompanied by the hydrogenolysis of the neopentyl andneopentylidene ligands, producing methane, ethane, propane, isobutaneand neopentane in the gas phase.

Another way of preparing the [Ta]_(s)—H tantalum hydride catalyst is asfollows:

the silica is dehydroxylated beforehand at a temperature greater than500° C. (up to 1100° C.), so as to bring about the appearance at thesurface of more or less strained siloxane bridges resulting from thecondensation of the hydroxyl groups;tris(neopentyl)neopentylidenetantalum Ta[—CH₂—CMe₃]₃[═CH—CMe₃] issublimed at 80° C. and reacts both with the remaining hydroxyl groupsand with the siloxane bridges according to:

Conversion of the neopentyl-neopentylidene complexes to the surfacetantalum hydrides takes place as above by treatment under hydrogen.

EXAMPLE 2

Preparation of the Tungsten Hydride Catalyst

The [W]_(s)—H surface tungsten hydride catalyst can be prepared in thefollowing way: tris(neopentyl)neopentylidynetungstenW[—CH₂—CMe₃]₃[≡C—CMe₃] is sublimed at 80° C. in a glass reactor oversilica dehydroxylated beforehand at 500° C., so as to graft the tungstencomplex by a reaction at 25° C. with one or more hydroxyl groups of thesilica surface. The mixture of the tungsten complexes which are obtainedis subsequently treated under hydrogen at atmospheric pressure at 150°C. for 15 h, so as to form the supported hydride species; this reactionis accompanied by the hydrogenolysis of the neopentyl and neopentylideneligands, producing methane, ethane, propane, isobutane and neopentane inthe gas phase.

EXAMPLE 3

Reaction for the Metathesis of Ethane:

The [Ta]_(s)—H tantalum hydride catalyst supported on silica (52.2 mg;4.89% Ta/SiO₂; 14.1 micromol of Ta) is prepared in situ in a glassreactor as described above. The reactor is placed under vacuum, thenfilled with ethane at atmospheric pressure (ethane/Ta=800) and heated at150° C. under batch conditions; the formation mainly of methane and ofpropane, as well as of butane and of isobutane, is then observedaccording to Table I:

TABLE I Reaction for the metathesis of ethane at 150° C. (ethane/Ta =800). Number of moles of hydrocarbons formed per mole of surfacetantalum Time (h) Rotations^(a) CH₄ C₃H₈ isobutane n-butane 2.5 3.1 1.591.43 0.02 0.07 22 12.2 8.13 5.13 0.09 0.11 82 46.4 26.54 20.28 0.63 0.73^(a)number of moles of ethane converted with respect to the tantalum

EXAMPLE 4

Reaction for the Metathesis of Propane:

The [Ta]_(s)—H catalyst (46.6 mg; 4.44% Ta/SiO₂; 11.4 micromol of Ta) isprepared as in Example 3 and then the reactor charged with propane atatmospheric pressure (propane/Ta=880) and heated at 150° C. under batchconditions. A mixture of methane, of ethane, of butane, of isobutaneand, in a smaller proportion, of pentane, of isopentane and of C₆homologues is gradually obtained according to the following Table 2.

EXAMPLE 5

Reaction for the Metathesis of Butane:

The [Ta]_(s)—H catalyst (53.3 mg; 4.78% Ta/SiO₂; 14.1 micromol of Ta) isprepared as in Example 3 and then the reactor is charged with butane atatmospheric pressure (butane/Ta=900) and heated at 150° C. under batchconditions. A mixture of ethane, of propane, of pentane and, in smallerproportions, of methane, of isobutane, of isopentane and of C₆homologues is gradually obtained according to the following Table 3.

EXAMPLE 6

Reaction for the Metathesis of Isobutane:

The [Ta]_(s)—H catalyst (66 mg; 9.52% Ta/SiO₂; 34.7 micromol of Ta) isprepared as in Example 3 and then the reactor is charged with isobutaneat atmospheric pressure (isobutane/Ta=244) and heated at 150° C. underbatch conditions. A mixture of methane, of ethane, of propane, ofneopentane, of isopentane and of 2-methylpentane and, in smallerproportions, of n-butane and of 2-methylhexane is gradually obtainedaccording to the following Table 4.

EXAMPLE 7

Reaction for the Metathesis of Propane at 150° C. over [W]_(s)—H/SiO₂Catalyst:

The [W]_(s)—H catalyst (55.7 mg; 4.96% W/SiO₂; 15.01 micromol of W)supported on silica is prepared as described above and then the reactoris charged with propane at atmospheric pressure (propane/W=790) andheated at 150° C. under batch conditions. A mixture of methane, ofethane, of isobutane, of butane, of pentane and, in a smallerproportion, of isopentane and of hexane is gradually obtained accordingto the following Table 5.

TABLE 2 Reaction for the metathesis of propane at 150° C. (propane/Ta =880) Number of moles of hydrocarbons formed per mole of surface tantalumTime (h) Rotations CH₄ C₂H₆ ibt^(a) nbut^(b) 2mbt^(c) npent^(d) C6^(e)C6^(e) nhex^(f)  5 14 3.32 5.95 1.05 4.34 0.34 0.70 20 36.3 8.58 15.833.03 10.72 0.94 1.77 43 43.8 9.39 18.07 3.58 12.91 1.13 2.22 0.11 0.090.32 ^(a)i-butane, ^(b)n-butane, ^(c)2-methylbutane, ^(d)n-pentane,^(e)isomers of n-hexane, ^(f)n-hexane.

TABLE 3 Reaction for the metathesis of butane at 150° C. (butane /Ta =900) Number of moles of hydrocarbons formed per mole of surface tantalumTime (h) Rotations CH₄ C₂H₆ C₃H₃ ibt^(a) 2mbt^(c) npent^(d) C6^(d)C6^(d) nhex^(e) 1.25 7 0.58 1.06 3.83 1.4 0.24 1.30 7.25 23.6 2.07 4.0014.76 2.21 0.95 5.34 23.25 40 2.38 6.24 22.71 2.55 1.15 7.86 0.32 1.163.13 138.25 66.5 2.78 10.66 36.33 3.00 1.97 14.29 0.58 0.32 5.72^(a)i-butane, ^(b)2-methylbutane, ^(c)n-pentane, ^(d)isomers ofn-hexane, ^(e)n-hexane.

TABLE 4 Reaction for the metathesis of isobutane at 150° C.(isobutane/Ta = 244) Number of moles of hydrocarbons formed per mole ofsurface tantalum Time (h) Rotations CH₄ C₂H₆ C₃H₈ n-C₄ ^(a) NpH^(b) i-C₅^(c) i-C₆ ^(d) i-C₇ ^(e)  3 3.3 1.38 0.87 1.33 0.15 0.3 0.44 0.27 0.0423 9.5 2.23 3.28 2.38 0.08 0.4 1.79 1.53 0.23 47 11.5 2.71 4.96 2.950.09 0.65 2.02 1.62 0.15 ^(a)n-butane, ^(b)neopentane, ^(c)isopentane,^(d)2-methylpentane, ^(e)2-methylhexane.

TABLE 5 Reaction for the metathesis of propane at 150° C. over[W]_(s)-H/SiO₂ catalyst (propane/W = 790) Number of moles ofhydrocarbons formed per Time mole of surface tantalum (h) Rotations CH₄C₂H₆ ibt^(a) nbut^(b) 2mbt^(c) npent^(d) nhex^(e) 2 3.4 0.09 2.04 0.061.25 0.14 4 6.7 0.12 4.16 0.11 2.42 0.33 20 11.7 0.24 7.49 0.25 3.9 0.070.62 0.09 ^(a)i-butane, ^(b)n-butane, ^(c)2-methylbutane, ^(d)n-pentane,^(e)n-hexane.

What is claimed is:
 1. Process for metathesis of linear or branched starting alkanes comprising reacting the linear or branched starting alkanes over a solid catalyst under the metathesis condition said alkanes, the solid catalyst comprising a solid oxide grafted with metal atoms in the form of hydrides dispersed over the solid oxide.
 2. Process according to claim 1, characterized in that the metal atoms of the solid catalyst in the form of hydrides exhibit high degrees of unsaturation.
 3. Process according to claim 1, characterized in that the solid catalyst is obtained from: a) an organometallic complex of formula (II) MR₈  (II)  where M is a transition metal selected from those of groups 5 and 6 of the Periodic Classification of the Elements, the R groups are identical or different, saturated or unsaturated, hydrocarbon-comprising ligands bonded to the M by one or more carbons, and a is less than or equal to the valency of M, which is 5 or 6; and b) an anhydrous solid oxide.
 4. Process according to claim 3, characterized in that the hydrocarbon-comprising ligands are C₁ to C₁₀ hydrocarbon-comprising ligands.
 5. Process according to claim 3, characterized in that the anhydrous solid oxide is obtained by heat treating the solid oxide to dehydrate and dehydroxylate the solid oxide.
 6. Process according to claim 3, characterized in that the solid catalyst is obtained by sublimation of the organometallic complex, followed by grafting the organometallic complex to the solid oxide, followed by hydrogenolysis of the carbon-comprising ligand to convert the metal to hydride.
 7. Process according to claim 6, characterized in that the temperature of the sublimation step is about 80° C.
 8. Process according to claim 6, characterized in that the sublimation is carried out under vacuum at a temperature between 50 and 15° C.
 9. Process according to claim 6, characterized in that the grafting reaction is carried out at a temperature greater than or equal to ambient temperature.
 10. Process according to claim 6, characterized in that, instead of a sublimation, the dispersion and the grafting are carried out starting with a solution of the organometallic complex in an organic solvent and by bringing this solution into contact with the solid oxide.
 11. Process according to claim 6, characterized in that the hydrogenolysis is carried out in the presence of hydrogen under a pressure of between 10⁻² and 100 bar, at a temperature of between 25 and 400° C., and for a period of time ranging from 1 h to 24 h.
 12. Process according to claim 11, characterized in that the pressure of the hydrogenolysis is atmospheric pressure.
 13. Process according to claim 12, characterized in that the temperature of the hydrogenolysis is about 150° C.
 14. Process according to claim 13, characterized in that the pressure of the hydrogenolysis is atmospheric pressure.
 15. Process according to claim 1, characterized in that the metal atoms are selected from the group consisting of tantalum, tungsten, and chromium.
 16. Process according to claim 1, characterized in that the solid oxide is selected from the group consisting of silica, alumina, silica-alumina, niobium, oxide, and zeolites.
 17. Process according to claim 16, characterized in that the solid catalyst is a tantalum, tungsten, or chromium hydride grafted to silica or silica-alumina.
 18. Process according to claim 1, characterized in that the metathesis reaction is carried out at a temperature of between 25 and 300° C.
 19. Process according to claim 18, characterized in that the temperature is between 100 and 200° C.
 20. Process according to claim 1, characterized in that the metathesis reaction is carried out by passing the alkane or alkanes in the gas phase over the solid catalyst.
 21. Process according to claim 20, characterized in that the metathesis reaction is carried out by passing the alkane or alkanes in the gas phase at a pressure greater than or equal to atmospheric pressure but less than or equal to the condensation pressure of the alkane or of the heaviest alkane when there are several starting alkanes.
 22. Process according to claim 1, characterized in that the reaction is carried out under a pressure of between 10⁻² and 100 bar.
 23. Process according to claim 22, characterized in that the reaction is carried out starting from atmospheric pressure.
 24. Process according to claim 1, characterized in that the metathesis reaction is carried out with the solid catalyst in suspension in a liquid phase of the alkane or alkanes.
 25. Process according to claim 1, characterized in that the metathesis reaction is carried out in the presence of at least one inert gas.
 26. Process according to claim 25, characterized in that the inert gas is selected from the group consisting of nitrogen, helium, and argon.
 27. Process according to claim 1, characterized in that the starting alkane or alkanes is/are selected from the group consisting of linear C₂-C₃₀ alkanes, branched C₄-C₃₀ alkanes, and cyclic hydrocarbons substituted by at least one linear or branched alkane chain.
 28. Process according to claim 27, characterized in that the cyclic hydrocarbons are aromatic rings or saturated rings.
 29. Process according to claim 27, characterized in that the hydrocarbon is a substituted saturated ring according to the formula (III)

where x is greater than or equal to 2 and y is greater than or equal to
 0. 30. Process according to claim 29, characterized in that x is between 2 and
 20. 31. Process according to claim 29, characterized in that y is between 0 and
 29. 32. Process according to claim 31, characterized in that x is between 2 and
 20. 33. Process according to claim 27, characterized in that the alkane or alkanes is/are selected from the group consisting of ethane, propane, butane, pentane, isobutane, isopentane, 2-methylpentane, 3-methylpentane and 2,3-dimethybutane.
 34. Process according to claim 1, characterized in that at least two alkanes selected from linear or branched alkanes and cyclic hydrocarbons substituted by at least one linear or branched chain are reacted together. 